Clever Top/Bottom Two-piece Design with Integral Spinal Cords/Alignment Housing for Perfect Fit with Barrel Nut and Round Front Cap * Made from Aircraft Aluminum with Precision CNC Machining and Excellent Anodizing/Engraving * Fits Car. Length Model 4/15 and Provides Four Picatinny Rails Each with 14 Slots, Great Zero-retention Capability for All Accessories Installed on the Rails * Easy Installation with No Modification to the Barrel, Proudly Made in USA with Superb Design and Production, OD Green Rubber Rail Guards Included * This quad rail system is designed to fit with standard AR15 gas tube. The compatibility with any special piston system is not guaranteed.